Generally, production of a pneumatic tire is carried out by setting a molded green tire in a tire vulcanizer and applying heat and pressure from both the inside and the outside of the green tire to vulcanize it.
Specifically, while heating and pressurizing the green tire from the outside with a vulcanization mold, a bladder for vulcanizing tire (hereinafter simply referred to as “bladder”) disposed in the lumen portion of the green tire is expanded by supplying a heating and pressing medium for heating and pressing the raw tire from the inside (Patent Document 1).
If a void such as air remains in the bladder and the bladder is used repeatedly with expansion and contraction, it may cause breakage and cracks due to fatigue and it may puncture and shorten the life (bladder life).
Therefore, at the time of manufacturing the bladder, when the kneaded rubber composition for a bladder (hereinafter also simply referred to as “rubber composition”) is extruded, for removing voids inside the resultant rubber member caused by the air entrainment at the time of introduction or the volatile component the rubber member, extrusion molding is carried out while sucking a gas component by vacuum during the extrusion operation (Patent Document 2). Thereby, it is possible to manufacture a bladder by molding homogeneous rubber without porous.